UTP .alpha.-D-glucose-1-phosphate uridylyl transferase, EC 2.7.7.9, (UGPase) is one of the key enzymes of carbohydrate metabolism. In photosynthetic tissue, UGPase converts glucose-1-phosphate to UDP-glucose which is a substrate for sucrose biosynthesis. Xu et al., Plant Physiol. 90:635-642 (1989).
UGPase activity is also associated with non-photosynthetic sink tissues such as the potato tuber. When sucrose is delivered to sink tissues, it is cleaved by sucrose synthase to UDP-glucose and fructose. UGPase then converts the UDP-glucose to glucose-1-phosphate. At this point, the hexose phosphate enters the amyloplast and serves as substrate for AGPase, and subsequently starch synthesis. Under stress conditions, starch is degraded and glucose-1-phosphate is released from the amyloplast and can then enter the same cytoplasmic sucrose biosynthetic pathway involving UGPase described above.
UGPase has been isolated and characterized from potato tubers (Nakano et al., J Biochem. 106: 528-532 (1989)). In addition, cDNA encoding this enzyme has been cloned and sequenced (Katsube et al., J Biochem. 108: 321-326 (1990)).
There is a need for a variety of different promoters to be used in the genetic engineering of plants. In particular, tissue-specific promoters which can drive expression of desired genes in particular tissues. The present invention addresses these and other needs.